1. Field of the Invention
The present invention relates to an apparatus for carrying bottles in a bottle making machine, and more precisely it relates to an improved pusher which is usually called 90.degree. pusher for conveying bottles onto a conveyer perpendicular to the direction of the movement of the bottles.
2. Description of the Related Art
In a bottle making machine, molded bottles (bottle bodies) are moved onto a dead plate to be cooled by the air and are then conveyed to a subsequent station. To carry the bottles to the subsequent station, the bottles are brought onto a conveyor which is located on one side of the dead plate by a pusher. The pusher rotates by about 90.degree. to move the bottles onto the conveyer and, accordingly, is called a 90.degree. pusher, in the field of the invention.
The reciprocal angular movement (swing movement) of the pusher does not take place at a constant angular velocity. Namely, for example, at the beginning of the swing movement of the pusher, the speed of the movement is relatively low, so that the bottle bodies are prevented from falling down when the pusher comes into contact with the bottle bodies. During the conveyance of the bottle bodies, the speed of the swing movement of the pusher is accelerated to increase the conveyance efficiency of the bottle bodies.
At this end, a rotational drive shaft of the pusher which rotates at a constant speed is provided with a cam which has a predetermined profile so as to vary the angular speed of the drive shaft.
However, in this type of speed control apparatus with the cam attached to the drive shaft of the pusher, it is necessary to exchange the cam, in accordance with shapes of the bottle bodies or the feed speed of the conveyer etc. To prepare a large number of and different kinds of cams is troublesome and costly.
On the other hand, in a bottle making factory, a plurality of independent molding apparatuses are usually provided along multiple manufacturing lines. Generally, the cams for different manufacturing lines have different angular phases. Accordingly, in order to change the number of lines which actually operate, it is necessary to adjust the angular phases of the cams in the manufacturing lines. This is, however, a troublesome operation. In addition, the operation also needs to stop the operation of the associated manufacturing lines. Furthermore, the pusher having the cam which is mechanically driven makes it difficult to realize a completely automatic bottle making system.
The primary object of the present invention is, therefore, to provide an apparatus for carrying bottles in a bottlemaking machine, in which the speed of the angular movement of the pusher can be controlled by an electrical signal, so that the control of the angular movement of the pusher becomes easier, resulting in a realization of a completely automatic bottle making system.
To achieve the object mentioned above, according to the present invention, there is provided an apparatus for carrying bottles in a bottle making machine, having a pusher for moving the bottles and a servomotor for reciprocally swinging the pusher within a predetermined angular displacement to move the bottles along an archwise track onto a conveyer, comprising means for emitting signals for the start and stop of the servomotor at a predetermined time, servo-control means for supplying a drive current to the servomotor with a predetermined change of time, in accordance with the start and stop signals to the servomotor to control the angular velocity thereof and for stopping the supply of the drive current to the servomotor when the servomotor is subject to an excess load, so that the drive current exceeds a predetermined value, and an AC servomotor which is driven by the drive current of the servo-control means.
With this arrangement of the invention, the start and stop of the operation of the servomotor and the change of the angular velocity of the pusher during operation can be automatically controlled at a predetermined cycle and at a predetermined time. If an excess torque (load) is applied to the servomotor for some reason, the drive current increases in accordance with an increase of the torque (load). When the drive current exceeds a predetermined value, the supply of the drive current is stopped to prevent the servomotor from being damaged.